COLUMN ONE : Swiss Open the Vaults of Secrecy : Long famous for asking no questions, the Alpine nation's bankers--at times prodded by new laws--are rebuffing shady clients, returning ill-gotten gains and helping authorities counter crime.

ZURICH, Switzerland — The South American drug lord strode into one of the famously discreet banks here recently with a large cash deposit. Expecting a simple transaction, he was, instead, questioned for two hours, then shown the door, still carrying his cash-stuffed suitcase.

"I'm sorry, but you aren't the right customer for this bank," the banker told him, according to someone familiar with the incident. Even a narcotics agent, working undercover in the drug lord's entourage, had to work to contain his surprise.

As that rebuff suggests, the days of no-questions-asked deposits in Swiss banks are fast disappearing.

Not only are banks turning away suspiciously wealthy customers, but for the past year they have been voluntarily reporting some to the authorities, under a special exception to the 61-year-old banking secrecy law.

In fact, Swiss bankers are making many changes in the way they do business.

They are cooperating with foreign governments more often, most recently in the case of late Philippine dictator Ferdinand Marcos' multimillion-dollar Swiss assets. And beginning next year, Swiss banks will make it easier for the heirs of deceased customers such as Holocaust victims to apply for family assets held in Swiss accounts.

"Bankers are becoming much more conscious of their moral responsibilities," said Silvia Matile-Steiner, an attorney with the Swiss Bankers Assn. in Basel. "We want to keep our image as a safe place but also as an honest place."

Or as an American diplomat in Switzerland put it: "They've got enough clean money without needing dirty money. The new rule for bankers is: If you take dirty money, you're in trouble."

The numbered account still lives. Although, these days, all the owners of those accounts are known to the bank, their identities held close to the executive vest and far from the eyes of tellers--and investigators.

Largely as a result, millions of dollars still flow into this banking haven from Third World dictators, tax-evading foreigners and rich folks trying to hide their nest eggs from mercenary heirs.

"Money we receive because the customer lacks confidence in his own country? It's not a problem," said Christian Frey, an economist at the nation's largest bank, the Union Bank of Switzerland. "We cannot be responsible for the instability of other countries."

But other practices are changing, if slowly.

Banks still refuse to divulge information on customers sought by foreign law enforcement agencies for tax evasion, because that is not a crime in Switzerland. Yet they now are cooperating on cases of insider trading, which became a Swiss crime in 1988, and on money laundering, which was criminalized here in 1990.

The most important change has been the 1994 law that allows bankers to report suspicious customers. Before, bankers were legally bound to maintain customer confidentiality even in suspicious cases.

Now the Swiss federal prosecutor wants a stronger law, one that would require banks to report such cases. To no one's surprise, the banks vociferously oppose it, arguing that it would undermine their special relationship with customers.

Still, in the banking center of Zurich, the country's largest city, authorities have received 26 reports of shady customers in the past year; nine of the cases led to prosecutions.

A senior manager of Union Bank of Switzerland is also under investigation for allowing a Colombian couple to make $200 million in deposits. The couple had said the money was from their South American hotels, but the cash deposits suggest drug money. And the authorities contend that the banker should have known.

All this is part of a broad move to polish the image of Swiss banking, an effort especially evident in two recent announcements.

In August, Switzerland agreed to turn over $500 million of Marcos' assets to the Philippine government.

Although the banks have appealed the decision, lawyers say that is just a formality to protect the banks from competing claims for the money. The lawyers say the banks intend to return the assets eventually, and the Philippine government is negotiating with human rights groups to divide the money.

In September, Swiss banks revealed that they have about $37 million in 893 deposit accounts that were opened before the end of World War II and have been dormant since 1985. At least some of that money may belong to Holocaust victims.

Swiss officials have tried to dampen speculation that billions of dollars from Holocaust victims remain in the country.

"I can understand people thinking their relatives may have kept some money in Switzerland, but I don't know where they get this figure," attorney Matile-Steiner said. "It is highly exaggerated."